Method and device for determining parameters of near-surface layer medium in wafer grinding scenario

Abstract

Provided in the present invention are a method and device for determining parameters of a near-surface layer medium in a wafer grinding scenario. The method comprises: acquiring an actually measured spectrum in the state where the surface of a wafer has a first-type layer and a second-type layer, wherein the wafer comprises a wafer substrate and a wafer film, parameters of the wafer substrate and the wafer film are known parameters measured in advance, and the second-type layer is located between the first-type layer and the wafer film; using a spectral calculation model having parameters of the first-type layer and the second-type layer to generate theoretical spectra under different given parameters of the second-type layer; and on the basis of the theoretical spectra and the actually measured spectrum, determining a parameter range of the second-type layer.

Description

Methods and equipment for determining parameters of near-surface layer media in wafer grinding scenarios Technical Field

[0001] This invention relates to the field of wafer parameter measurement, and more specifically to a method and device for determining the parameters of the near-surface layer medium in a wafer grinding scenario. Background Technology

[0002] In wafer manufacturing, with the upgrading of process technology and the shrinking of wire and gate dimensions, the requirements for the non-uniformity of the wafer surface in lithography are becoming increasingly stringent. CMP (chemical mechanical polishing) technology has been widely applied to wafers in recent decades. CMP demands extremely high polishing precision, requiring precise thickness measurement of the wafer thin film to meet these requirements. Due to the complex CMP processing environment, current technology cannot achieve real-time, in-situ optical non-contact measurement of the wafer thin film. Instead, offline measurement and other endpoint measurements are performed by removing the wafer from the CMP process. However, endpoint measurements can only detect the grinding endpoint and cannot be performed in real-time.

[0003] In implementing this embodiment, during the non-contact, in-situ real-time optical measurement of wafer thin films, various media, such as glass, PU, ​​and polishing fluid, exist between the wafer and the probe. Under the influence of these media, the reflectance spectrum undergoes a "distortion" phenomenon. The theoretical spectrum of the film under test (wafer thin film) in the prior art cannot describe this "distortion" phenomenon, thus preventing the prior art from accurately measuring the accurate thickness of the film under test.

[0004] Based on the deformed spectrum, the inventors discovered that a near-surface structural layer exists on the wafer during in-situ measurement of wafer film thickness. This near-surface structural layer causes the phenomenon of deformed spectra. The thickness of this near-surface layer affects the accuracy of the theoretical spectrum of the film under test under the "deformation" phenomenon, and thus affects the accuracy of measuring the film thickness under complex environments. Therefore, how to determine the film thickness of this near-surface layer is a technical problem that urgently needs to be solved in the prior art. Summary of the Invention

[0005] In view of this, this application provides a method for determining the parameters of the near-surface layer dielectric in a wafer grinding scenario, including:

[0006] Measured spectra of a wafer surface having a first type of layer and a second type of layer are obtained, wherein the wafer includes a wafer substrate and a wafer thin film, the parameters of the wafer substrate and the wafer thin film are known parameters measured in advance, and the second type of layer is located between the first type of layer and the wafer thin film;

[0007] Using a spectral calculation model with parameters of the first and second types of layers, theoretical spectra are generated for different given parameters of the second type of layer.

[0008] The parameter range of the second type of layer is determined based on the theoretical spectrum and the measured spectrum.

[0009] Optionally, the theoretical spectrum and the measured spectrum each include a curve showing the relationship between wavelength and reflectance.

[0010] Optionally, determining the parameter range of the second type of layer based on the theoretical spectrum and the measured spectrum includes:

[0011] Get the matching threshold;

[0012] Calculate the matching degree between the theoretical spectrum and the measured spectrum under different given parameters of the second type layer, and determine the parameter range based on the parameters of the second type layer corresponding to the theoretical spectrum whose calculated matching degree meets the matching degree threshold.

[0013] Optionally, the parameters of the second type of layer include refractive index, thickness, and a mapping relationship between the refractive index and the thickness based on the spectral calculation model.

[0014] Optionally, determining the parameter range for the second type of layer includes:

[0015] Based on the mapping relationship between the refractive index and the thickness, and when the matching degree between the theoretical spectrum and the measured spectrum meets the matching degree threshold, the range of refractive index and the range of thickness corresponding to the second type of layer are solved.

[0016] Optionally, the matching degree is the goodness of fit, and the goodness of fit K between the theoretical spectrum and the measured spectrum is calculated as follows:

[0017] Where x 1i x represents the value of the i-th data point in the measured spectrum. 2i This represents the value of the i-th data point in the theoretical spectrum given the parameters of the second type of layer, where n represents the number of data points.

[0018] Optionally, the spectral calculation model includes the following parameters:

[0019] The refractive index n1 of the first type layer, the refractive index n2 of the wafer thin film, the refractive index n3 of the wafer substrate, the refractive index n4 of the second type layer, and the thickness d4 of the second type layer.

[0020] Optionally, the spectral calculation model includes:

[0021] R = r·r *

[0022] Where r is the total reflection coefficient determined based on n1, n2, n3, n4, and d4. * Let r be the conjugate complex number, and R be the reflectivity.

[0023] Alternatively, the total reflection coefficient r can be calculated as follows:

[0024] Calculate the reflection coefficient of the interface of each layer using n1, n2, n3, and n4;

[0025] The phase thickness θ of the wafer thin film is calculated using n2, wavelength λ, and wafer thin film thickness d2.

[0026] The phase thickness α of the second type layer is calculated using n4, wavelength λ, and thickness d4;

[0027] The total reflection coefficient r is calculated using the reflection coefficients, phase thickness α, and phase thickness θ of each layer's interface.

[0028] Optionally, the reflection coefficients of the interfaces of each layer include the reflection coefficient r2 of the interface between the wafer thin film and the wafer substrate, the reflection coefficient r3 of the interface between the first type layer and the second type layer, and the reflection coefficient r4 of the interface between the second type layer and the wafer thin film.

[0029] Optionally, calculating the reflection coefficient of the interface of each layer includes:

[0030] The reflection coefficient r2 at the interface between the wafer thin film and the wafer substrate is calculated using n2 and n3;

[0031] The reflection coefficient r3 at the interface between the wafer thin film and the wafer substrate is calculated using n1 and n4.

[0032] The reflection coefficient r4 at the interface between the wafer thin film and the wafer substrate is calculated using n2 and n4.

[0033] Optionally, the total reflectance r is calculated, including:

[0034] Calculate the equivalent interface reflection coefficient r using θ, r2, and r4. 等效 ;

[0035] Using α, r3 and r 等效 Calculate the total reflection coefficient r.

[0036] Optionally, the parameter range of the second type of layer is used to generate a spectral library for in-situ measurement of wafer film thickness using optical non-contact reflectance method.

[0037] Accordingly, the present invention provides a parameter determination device for near-surface layer media in a wafer grinding scenario, comprising: a processor and a memory connected to the processor; wherein, the memory stores instructions executable by the processor, the instructions being executed by the processor to cause the processor to perform the above-described parameter determination method for near-surface layer media in a wafer grinding scenario.

[0038] According to the near-surface layer dielectric parameter determination method of the present invention, a wafer with a known wafer film thickness is used as the measurement object, and the wafer is placed in a grinding scenario. The spectrum of the wafer is measured under the condition that the grinding surface has a first type of layer and a second type of layer. The spectrum exhibits distortion, which is consistent with the actual model scenario. Then, the theoretical spectrum under different given wafer parameters is calculated through the constructed spectral calculation model. The spectrum also reflects the influence of the first type of layer and the second type of layer on reflectivity. By comparing the theoretical spectrum and the measured spectrum, the parameters of the second type of layer of the measurement object can be deduced. This result can be used to construct a reference spectral library, thereby improving the accuracy of optical non-contact measurement of wafer film thickness. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 shows a measured spectral curve in an embodiment of the present invention;

[0041] Figure 2 is a comparison diagram of the theoretical spectral curve and the measured spectral curve in the embodiment of the present invention. Detailed Implementation

[0042] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] This invention provides a method for determining the parameters of the near-surface layer dielectric in a wafer grinding scenario. This method can be executed by electronic devices such as computers or servers, and includes the following operations:

[0045] Measured spectra of a wafer surface with a first type of layer and a second type of layer were obtained, wherein the wafer includes a wafer substrate and a wafer thin film. Having a first type of layer and a second type of layer refers to placing the wafer in a grinding environment, adding a polishing slurry to the grinding surface of the wafer, causing the formation of a first type of layer and a second type of layer on the surface. The first type of layer and the second type of layer are located between the bulk water and the wafer thin film, and the second type of layer is located between the first type of layer and the wafer thin film. The first type of layer can be an air-formed layer.

[0046] The measured spectrum can be data on the correspondence between wavelength and reflectance collected using a spectrometer, which can be expressed as a curve; that is, the measured spectrum can be a curve showing the correspondence between wavelength and reflectance. In this embodiment, those skilled in the art can modify the correspondence between wavelength and reflectance according to actual needs. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. However, obvious variations or modifications derived therefrom are still within the protection scope of this invention.

[0047] In this embodiment, the wafer includes a wafer substrate (silicon) and a wafer thin film (silicon oxide). The material of the wafer substrate, the material of the wafer thin film, and the thickness of the wafer thin film are known parameters that have been measured beforehand. The thickness of the wafer thin film can be measured offline (e.g., using a microspectral thickness gauge) before a polishing slurry is added to the surface. Figure 1 shows the measured spectral curve for a wafer thin film thickness of 700 nm, where the wavelength range is 200–800 nm. This curve represents the reflectivity of light within this wavelength range.

[0048] Using a spectral calculation model with parameters for the first and second types of layers, theoretical spectra are generated for different given parameters of the second type of layer.

[0049] Optionally, the spectral calculation model constructed in this embodiment involves the refractive index n1 of the first type of layer, the refractive index n2 of the wafer thin film, the refractive index n3 of the wafer substrate, the refractive index n4 of the second type of layer, and the thickness d4 of the second type of layer.

[0050] n1, n2, and n3 can be obtained by instrument measurement and are fixed values, while d4 and n4 are parameters that need to be given. The range of wavelength λ is consistent with the wavelength range in the measured spectrum.

[0051] For example, d4 = [0.001, 0.002, 0.003, ..., 3] represents a value range of 0.001 to 3, with a step size of 0.001 and units in nm. Then, using the constructed spectral calculation model, the reflectance for wavelengths from 200 to 800 nm can be calculated for each d4. That is, when d4 = 0.001, the reflectance for wavelengths λ = [200, 800] is calculated, and the resulting theoretical spectrum is denoted as R.0.001 When d4 = 0.002, the reflectance at wavelength λ = [200, 800] is calculated, and the resulting theoretical spectrum is denoted as R. 0.002 When d4 = 3, the reflectance of wavelength λ = [200, 800] is calculated, and the resulting theoretical spectrum is denoted as R3.

[0052] The parameter range of the second type layer is determined based on theoretical and measured spectra. In the spectral calculation model, d4 and n4 are independent variables. The calculated theoretical spectra differ depending on the values ​​of d4 and n4. By comparing these theoretical spectra with the measured spectra shown in Figure 1, the values ​​of d4 and n4 can be derived. In other words, a smaller range or a single value can be determined from the given ranges of d4 and n4.

[0053] By comparing all theoretical spectra with the measured spectra one by one, one or more theoretical spectra that are most similar to the measured spectra can be identified. Figure 2 shows the curves of the theoretical spectrum (dashed line) and the curves of the measured spectrum (solid line). If the similarity between these two curves is considered to be high enough, the thickness and refractive index of the second type layer of the theoretical spectrum can be determined.

[0054] There are various methods for calculating the similarity between two curves, and various metrics for measuring similarity or matching degree, such as the similarity method, nonlinear regression method, and FFT method. One approach is to preset an absolute threshold, classifying all theoretical spectral curves with similarity within the threshold range as sufficiently similar. The corresponding d4 values ​​of these curves represent the thickness range of the second-type layer, and the corresponding n4 values ​​represent the refractive index range of the second-type layer. Alternatively, a relative threshold can be set, comparing the similarity between all theoretical and measured spectral curves to select one or more curves with the highest relative similarity. The corresponding d4 and n4 values ​​represent the actual thickness or parameter range of the near-surface layer medium.

[0055] According to the near-surface layer dielectric parameter determination method of the present invention, a wafer with a known wafer thin film thickness is used as the measurement object, and it is placed in a grinding scenario. Under the condition that the grinding surface has a first type of layer and a second type of layer, its spectrum is measured. The curve exhibits distortion, which is consistent with the situation in the actual model scenario. Then, the theoretical spectrum under different given parameters of the second type of layer is calculated through the constructed spectral calculation model. This spectrum also reflects the influence of the first type of layer and the second type of layer on reflectivity. By comparing the theoretical spectrum and the measured spectrum, the parameters of the second type of layer of the measurement object can be deduced. This result can be used to construct a reference spectral library, thereby improving the accuracy of optical non-contact measurement of wafer thin film thickness.

[0056] The aforementioned spectral calculation model can be improved upon existing spectral calculation models that do not incorporate a second type of layer structure. Compared to existing technologies, the physical structure in this solution adds a second type of layer between the wafer thin film and the first type of layer.

[0057] For example, a specific spectral calculation model could be: R = r·r *

[0058] Where r is the total reflection coefficient determined based on n1, n2, n3, n4, and d4. * Let R be the conjugate complex number of r, and R be the reflectance. Based on the above model, for each given d⁴ and n⁴, R can be calculated for each λ, thereby obtaining the theoretical spectral data for each given second-type layer parameter.

[0059] In one embodiment, the total reflection coefficient r is calculated as follows:

[0060] The reflection coefficients of the interfaces of each layer are calculated using n1, n2, n3, and n4; the phase thickness θ of the wafer thin film is calculated using n2, wavelength λ, and wafer thin film thickness d2; the phase thickness α of the second type layer is calculated using n4, wavelength λ, and thickness d4; and the total reflection coefficient r is calculated using the reflection coefficients of the interfaces of each layer, phase thickness α, and phase thickness θ.

[0061] Furthermore, the reflection coefficients of the interfaces of each layer include the reflection coefficient r2 of the interface between the wafer thin film and the wafer substrate, the reflection coefficient r3 of the interface between the first type layer and the second type layer, and the reflection coefficient r4 of the interface between the second type layer and the wafer thin film.

[0062] The calculation of the reflection coefficients at the interfaces of each layer includes: calculating the reflection coefficient r2 at the interface between the wafer thin film and the wafer substrate using n2 and n3; calculating the reflection coefficient r3 at the interface between the wafer thin film and the wafer substrate using n1 and n4; and calculating the reflection coefficient r4 at the interface between the wafer thin film and the wafer substrate using n2 and n4.

[0063] Calculate the total reflection coefficient r, including: calculating the equivalent interface reflection coefficient r using θ, r2, and r4. 等效 Using α, r3 and r 等效 Calculate the total reflection coefficient r.

[0064] As an example, the reflection coefficient can be calculated as follows:

[0065] The phase thickness θ can be calculated as follows:

[0066] The phase thickness α can be calculated as follows:

[0067] The equivalent interface reflection coefficient r can be calculated as follows: 等效 :

[0068] The total reflection coefficient r can be calculated as follows:

[0069] Where i is the imaginary unit and e is the natural constant.

[0070] The above calculation formulas can be modified in simple ways according to actual needs, such as adding preset coefficients or weights to one of the formulas. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all the calculation formulas here. However, any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

[0071] In one embodiment, determining the parameter range of the second type of layer based on theoretical and measured spectra includes:

[0072] A matching threshold is obtained, specifically a value given manually. The matching degree between the theoretical spectrum and the measured spectrum under different given parameters of the second type layer is calculated. The parameter range is determined based on the parameters of the second type layer corresponding to the theoretical spectrum whose calculated matching degree meets the matching threshold.

[0073] By using the above method of screening theoretical spectra based on matching degree thresholds, the accuracy of the near-surface layer medium thickness results can be controlled manually.

[0074] Furthermore, in this embodiment, the parameters of the second type of layer include refractive index n4 and thickness d4, and there is a mapping relationship between n4 and d4. Based on the mapping relationship between refractive index n4 and thickness d4, and when the matching degree between the theoretical spectrum and the measured spectrum meets the matching degree threshold, the refractive index range and thickness range corresponding to the second type of layer are solved.

[0075] In one embodiment, the goodness of fit K between the theoretical spectrum and the measured spectrum is calculated, and the goodness of fit K is used as a measure of the matching degree between the two curves:

[0076] Where x 1i x represents the value of the i-th data point in the measured spectrum. 2i This represents the value of the i-th data point in the theoretical spectrum given the parameters of the second type layer, where n represents the number of data points.

[0077] The above method is the least squares fitting method. The goodness of fit K is also called the Euclidean distance between the two spectra. The larger the goodness of fit K, the lower the similarity / matching degree, and the smaller the goodness of fit K, the higher the similarity / matching degree.

[0078] By setting a preset threshold to determine the fit, the parameter range of the second type of layer can be controlled. The smaller the K value, the higher the similarity between the two spectra, resulting in higher resolution for the film thickness detection and a smaller parameter range for the second type of layer.

[0079] When using thickness d4 and refractive index n4 to generate a reference spectral library, any value from the above range can be selected as a fixed parameter. Experimental data shows that when the values ​​of d4 and n4 are within a suitable range, different values ​​have little impact on the spectrum, or this can be interpreted as the high similarity between spectra generated by different values ​​within this range. Therefore, selecting any value as a fixed parameter is feasible.

[0080] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0081] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more blocks of the flowchart illustrations and / or one or more blocks of the block diagrams.

[0082] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0083] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for determining the parameters of the near-surface layer dielectric in a wafer grinding scenario, characterized in that, include: Measured spectra of a wafer surface having a first type of layer and a second type of layer are obtained, wherein the wafer includes a wafer substrate and a wafer thin film, the parameters of the wafer substrate and the wafer thin film are known parameters measured in advance, and the second type of layer is located between the first type of layer and the wafer thin film; Using a spectral calculation model with parameters of the first and second types of layers, theoretical spectra are generated for different given parameters of the second type of layer. The parameter range of the second type of layer is determined based on the theoretical spectrum and the measured spectrum.

2. The method according to claim 1, characterized in that, The theoretical spectrum and the measured spectrum each include curves showing the relationship between wavelength and reflectivity.

3. The method according to claim 1, characterized in that, Determining the parameter range of the second type of layer based on the theoretical spectrum and the measured spectrum includes: Get the matching threshold; Calculate the matching degree between the theoretical spectrum and the measured spectrum under different given parameters of the second type layer, and determine the parameter range based on the parameters of the second type layer corresponding to the theoretical spectrum whose calculated matching degree meets the matching degree threshold.

4. The method according to claim 3, characterized in that, The parameters of the second type of layer include refractive index, thickness, and the mapping relationship between the refractive index and the thickness based on the spectral calculation model.

5. The method according to claim 4, characterized in that, Determining the parameter range for the second type of layer includes: Based on the mapping relationship between the refractive index and the thickness, and when the matching degree between the theoretical spectrum and the measured spectrum meets the matching degree threshold, the range of refractive index and the range of thickness corresponding to the second type of layer are solved.

6. The method according to claim 3, characterized in that, The matching degree is the goodness of fit, and the goodness of fit K between the theoretical spectrum and the measured spectrum is calculated as follows: Where x 1i x represents the value of the i-th data point in the measured spectrum. 2i This represents the value of the i-th data point in the theoretical spectrum given the parameters of the second type of layer, where n represents the number of data points.

7. The method according to claim 1, characterized in that, The spectral calculation model includes the following parameters: The refractive index n1 of the first type layer, the refractive index n2 of the wafer thin film, the refractive index n3 of the wafer substrate, the refractive index n4 of the second type layer, and the thickness d4 of the second type layer.

8. The method according to claim 7, characterized in that, The spectral calculation model includes: R = r·r * Where r is the total reflection coefficient determined based on n1, n2, n3, n4, and d4. * Let r be the conjugate complex number, and R be the reflectivity.

9. The method according to claim 8, characterized in that, The total reflection coefficient r is calculated as follows: Calculate the reflection coefficient of the interface of each layer using n1, n2, n3, and n4; The phase thickness θ of the wafer thin film is calculated using n2, wavelength λ, and wafer thin film thickness d2. The phase thickness α of the second type layer is calculated using n4, wavelength λ, and thickness d4; The total reflection coefficient r is calculated using the reflection coefficients, phase thickness α, and phase thickness θ of each layer's interface.

10. The method according to claim 9, characterized in that, The reflection coefficients of the interfaces of each layer include the reflection coefficient r2 of the interface between the wafer thin film and the wafer substrate, the reflection coefficient r3 of the interface between the first type layer and the second type layer, and the reflection coefficient r4 of the interface between the second type layer and the wafer thin film.

11. The method according to claim 10, characterized in that, Calculating the reflection coefficient of each layer's interface includes: The reflection coefficient r2 at the interface between the wafer thin film and the wafer substrate is calculated using n2 and n3; The reflection coefficient r3 at the interface between the wafer thin film and the wafer substrate is calculated using n1 and n4. The reflection coefficient r4 at the interface between the wafer thin film and the wafer substrate is calculated using n2 and n4.

12. The method according to claim 10, characterized in that, The total reflectance r is calculated, including: Calculate the equivalent interface reflection coefficient r using θ, r2, and r4. 等效 ; Using α, r3 and r 等效 Calculate the total reflection coefficient r.

13. The method according to any one of claims 1-12, characterized in that, The parameter range of the second type of layer is used to generate the spectral library used for in-situ measurement of wafer film thickness using the optical non-contact reflectance method.

14. A device for determining the parameters of a near-surface layer medium in a wafer grinding scenario, characterized in that, include: A processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, the instructions being executed by the processor to cause the processor to perform the parameter determination method for near-surface layer media in a wafer grinding scenario as described in any one of claims 1-13.

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